Preparation of phosphonomethylated amino acids

ABSTRACT

A process for preparing phosphonomethylated amino acids comprising phosphonomethylating an N-sulfonylglycine derivative with formaldehyde and a phosphorus source to obtain a phosphonomethylated N-sulfonylglycine derivative which is then hydrolyzed to the corresponding phosphonomethylated amino acid, e.g., glyphosate, or the acid derivative. 
     The N-sulfonylglycine derivative can be prepared by reacting a sulfonic acid derivative with a haloacetic acid.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is a process for preparing phosphonomethylated amino acids, and, in particular, for preparing N-phosphonomethylglycine, otherwise known as glyphosate.

2. Related Information

Certain phosphonomethylated amino acids, e.g. glyphosate and its derivatives, are herbicides. Herbicides are useful for controlling or modifying plant growth. Glyphosate and its derivatives are effective in controlling or modifying growth in a wide variety of plant species, including broadleaves, grasses and sedge.

Because glyphosate and its derivatives are so important, new processes for making it and its derivatives faster, cheaper or in greater yields are constantly in demand. A new process for preparing glyphosate and its derivatives has now been discovered.

U.S. Pat. No. 4,439,373 (Nagubandi, Mar. 27, 1984) discloses a process for preparing phosphonomethylated amino acids comprising reacting a primary amino acid ester or salt with a carbon dioxide group to form a glycine carbamate compound then phosphonomethylating said amino compound to obtain a phosphonomethylated amino compound and acidifying said phosphonomethylated amino compound to expel carbon dioxide and yield a phosphonomethylated amino acid or acid derivative.

British Patent No. 1,413,137 (Beauhaire et al., Nov. 5, 1975) generally discloses the use of an emulsifiable oil in a process for the cold rolling of light metals. The reference specifically discloses the use of sodium and triethanol amine sulfoamido-acetate in this process.

A process for preparing a phosphonomethylated amino acid by phosphonomethylating a N-sulfonylglycine derivative then further hydrolyzing said derivative to obtain the phosphonomethylated amino acid would be advantageous.

It is an object of the present invention to provide a process for preparing phosphonomethylated amino acids.

Other objects and advantages of the present invention are shown throughout the specification.

SUMMARY OF THE INVENTION

In accordance with the present invention, it has now been discovered that phosphonomethylated amino acids can be prepared by a process which comprises: phosphonomethylating an N-sulfonylglycine derivative to obtain a phosphonomethylated N-sulfonylglycine derivative; and hydrolyzing said phosphonomethylated N-sulfonylglycine derivative to obtain a phosphonomethylated amino acid or acid derivative. The N-sulfonylglycine derivative is phosphonomethylated at the nitrogen.

The process is illustrated by the preparation of glyphosate or its derivatives, however other phosphonomethylated amino acids or their derivatives can be prepared by the process. In one preferred embodiment, the process comprises: (a) reacting sulfamic acid and chloroacetic acid in the presence of a base and at a temperature range of from about 0° C. to about 10° C. to form a N-sulfonylglycine derivative; (b) phosphonomethylating said N-sulfonylglycine derivative by reaction with formaldehyde and phosphorous acid in the presence of a solvent and with refluxing for about 1 to 3 hours; and (c) hydrolyzing said phosphonomethylated N-sulfonylglycine derivative by refluxing in the presence of a strong acid to form glyphosate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises a process for preparing phosphonomethylated amino acids. In this process, an N-sulfonylglycine derivative is phosphonomethylated, then the resulting product is hydrolyzed to obtain a phosphonomethylated amino acid or acid derivative.

The N-sulfonylglycine derivative used in this process can be prepared by the reaction of sulfamic acid and an haloacetic acid or ester.

The following reactions illustrate the present invention: ##STR1##

In reaction (1) sulfamic acid is reacted with a haloacetic acid derivative to form an N-sulfonylglycine derivative.

In reaction (2) the N-sulfonylglycine derivative is phosphonomethylated at the nitrogen using formaldehyde and a phosphorus source.

In reaction (3) the phosphonomethylated N-sulfonylglycine derivative is hydrolyzed to obtain a phosphonomethylated amino acid.

In reaction (1), X is an halide selected from the group consisting of chloride, bromide, and iodide. In reactions (1), (2) and (3), R¹ is selected from the group consisting of hydrogen and alkyl having 1 to 4 carbon atoms. A preferred haloacetic acid derivative is chloroacetic acid.

Reaction (1) preferably takes place in the presence of a suitable base. Suitable bases can include, for example, sodium hydroxide, sodium bicarbonate, sodium carbonate, pyridine and triethylamine.

It is desirable to carry out reaction (1) at or below room temperature, with a temperature range of from about 0° C. to about 10° C. being preferable. The mole ratio of the sulfamic acid to the haloacetic acid derivative can generally range from about a 1:5 ratio, with about a 1:3 ratio being desirable and about a 1:2 mole ratio being preferable.

The particular N-sulfonylglycine derivative resulting from reaction (1) will vary according to the specific haloacetic acid derivative used and according to the specific base used. For example, when the preferred chloroacetic acid is used in the presence of sodium hydroxide, NaO₃ SN(H)CH₂ CO₂ Na results. In this application N-sulfonylglycine and its derivatives are characterized as the N-sulfonylglycine derivative.

The N-sulfonylglycine derivative can be separated from the reaction mixture by filtration. Acidification with, for example, concentrated hydrochloric acid can convert the derivative into N-sulfonylglycine. The recovery of N-sulfonylglycine can be aided by the use of a solvent, for example, ethanol, and the recovered product can be washed with, for example, diethylether to enhance the purity of the product.

The phosphorus source used in reaction (2) is selected from the group consisting of: ##STR2## wherein R is selected independently each time it occurs from the group consisting of hydrogen, alkyl having 1 to 8 carbon atoms, inclusive; phenyl and substituted phenyl wherein the substitutents are selected from the group consisting of alkyl having 1 to 4 carbon atoms, inclusive; alkoxy having 1 to 4 carbon atoms, inclusive; and halogen. A preferred phosphorus source is phosphorous acid.

In reaction (2) the formaldehyde used can be in the form of aqueous formaldehyde or solid paraformaldehyde. If solid paraformaldehyde is used, water can be used as a solvent. The mole ratio of formaldehyde to the N-sulfonylglycine derivative should be at least 1:1. Excess amount of formaldehyde, up to a 3:1 mole ratio can be emloyed. Mole ratios greater than 3:1 are not desirable for economic reasons.

The N-sulfonylglycine derivative can be suspended in an organic solvent such as methanol. If this is done, it may be necessary to make the reaction mixture basic with a suitable base before adding formaldehyde to the protected amino compound. Suitable bases include but are not limited to sodium hydroxide, sodium methoxide and sodium ethoxide.

The phosphorous source can then be added to the reaction mixture. The mole ratio of the phosphorus source to the N-sulfonylglycine derivative should also be at least 1:1 and can range up to about 2:1. Greater amounts of the phosphorus source relative to the N-sulfonylglycine derivative are not economically desirable.

After the addition of the phosphorus source, the resulting reaction mixture is heated to reflux from about 80° C. to about 100° C. for at least 2 to 3 hours. A phosphonomethylated N-sulfonylglycine derivative results. This derivative can be separated by filtration.

In reaction (3) a phosphonomethylated N-sulfonylglycine derivative is hydrolyzed to prepare the desired phosphonomethylated amino acid or acid derivative. In this hydrolysis reaction, the derivative is heated preferably to reflux temperature in the presence of a suitable strong acid. Generally, a range of from about 4 moles to about 15 moles of acid can be used, with from about 4 moles to about 10 moles being desirable and about 4 moles to about 6 moles being preferable. Typically, at reflux temperatures, the reaction time ranges from about 1 hour to about 10 hours, with about 1 hour to about 5 hours being desirable and about 2 hours to about 3 hours being preferable. Suitable strong acids include, but are not limited to, hydrochloric acid, sulfuric acid and nitric acid. After refluxing, evaporation of the solvent yields a phosphonomethylated amino acid or acid derivative.

The following examples describe various embodiments of the invention. Other embodiments will be apparent to the skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specifications and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the claims which follow the examples.

EXAMPLE 1 Synthesis of N-Sulfonylglycine

Sulfamic acid (26.3 grams, 0.25 mole) was added to a solution of sodium hydroxide (40 grams, 1.0 mole) in water (25 mls) to form a reaction mixture. The reaction mixture was cooled then chloracetic acid (47.3 grams, 0.5 mole) dissolved in 15 mls of water was added. After 12 hours, the reaction mixture was acidified with concentrated HCl and a turbid mixture formed. Ethanol was then added to this turbid mixture which was then filtered. The resulting white solids were thoroughly washed with diethyl ether and the product obtained, N-sulfonylglycine, was used in the other steps of the process of this invention. The N-sulfonylglycine was identified by NMR and IR and the yield was 80% by weight.

EXAMPLE 2 Synthesis of Glyphosate via N-Sulfonylglycine

N-sulfonylglycine (5 grams, 0.032 mole), prepared in the prior example, was suspended in methanol (50 mls) and sodium methoxide (25% sodium hydroxide in methanol) was added to adjust the pH of the suspension to 8-9. Paraformaldehyde (1 gram, 0.033 mole) and trimethylphosphite (3.8 mls, 0.032 mole) were added to the suspension and the resulting reaction mixture was then refluxed. The pH was adjusted with sodium methoxide solution from time to time to maintain it between 8 and 9. After 5 hours, the solids present in the reaction mixture were separated and the filtrate was evaporated. The resulting residue was refluxed with concentrated HCl (25 mls). After 3 hours, the solvent was removed to obtain the product glyphosate. This product was isolated and the structure confirmed by H and ³¹ P NMR spectroscopy. 

What is claimed is:
 1. A process for preparing a phosphonomethylated amino acid comprising: phosphonomethylating an N-sulfonylglycine derivative to obtain a phophonomethylated N-sulfonylglycine derivative; and hydrolyzing said phosphonomethylated N-sulfonylglycine derivative to obtain a phosphonomethylated amino acid or acid derivative.
 2. The process of claim 1 wherein said N-sulfonylglycine derivative is phosphonomethylated by the use of formaldehyde and a phosphorus source.
 3. The process of claim 2 wherein said formaldehyde is used in the form of aqueous formaldehyde.
 4. The process of claim 2 wherein said formaldehyde is used in the form of paraformaldehyde.
 5. The process of claim 1 wherein said N-sulfonylglycine derivative is phosphonomethylated by adding at least 1 mole equivalent of formaldehyde and at least 1 mole equivalent of a phosphorus source to said N-sulfonylglycine derivative to form a reaction mixture; and then refluxing said reaction mixture to obtain a phosphonomethylated N-sulfonylglycine derivative.
 6. The process of claim 5 wherein said phosphonomethylation takes place in the presence of a solvent and a base.
 7. The process of claim 2 wherein said phosphorus source has the structure: ##STR3## wherein R is selected independently each time it occurs from the group consisting of hydrogen, alkyl having 1 to 8 carbon atoms, inclusive; phenyl and substituted phenyl wherein the substitutuents are selected from the group consisting of alkyl having 1 to 4 carbon atoms, inclusive; alkoxy having 1 to 4 carbon atoms, inclusive; and halogen.
 8. The process of claim 1 wherein said phosphonomethylated N-sulfonylglycine derivative is hydrolyzed in the presence of a strong acid.
 9. The process of claim 8 wherein said phosphonomethylated N-sulfonylglycine derivative is hydrolyzed by refluxing for about 1 to about 3 hours in the presence of a strong acid selected from the group consisting of hydrochloric acid, sulfuric acid and nitric acid.
 10. A process for preparing a phosphonomethylated amino acid comprising:(a) reacting a sulfamic acid derivative with haloacetic acid to form a N-sulfonylglycine derivative; (b) phosphonomethylating said N-sulfonylglycine derivative to obtain a phosphonomethylated N-sulfonylglycine derivative; and (c) hydrolyzing said phosphonomethylated N-sulfonylglycine derivative to obtain a phosphonomethylated amino acid or acid derivative.
 11. The process of claim 10 wherein the reaction of step (a) is carried out in the presence of a base.
 12. The process of claim 11 wherein the reaction of step (b) is carried out at a temperature from about 0° C. to about 10° C.
 13. The process of claim 10 wherein said N-sulfonylglycine derivative is phosphonomethylated by the use of formaldehyde and a phosphorus source.
 14. The process of claim 10 wherein said N-sulfonylglycine derivative is phosphonomethylated by adding at least 1 mole equivalent of formaldehyde and at least 1 mole equivalent of a phosphorus source to said N-sulfonylglycine derivative to form a reaction mixture; and then refluxing said reaction mixture to obtain a phosphonomethylated N-sulfonylglycine derivative.
 15. The process of claim 13 wherein said phosphorus source has the structure: ##STR4## wherein R is selected independently each time it occurs from the group consisting of hydrogen, alkyl having 1 to 8 carbon atoms, inclusive; phenyl and substituted phenyl wherein the substituents are selected from the group consisting of alkyl having 1 to 4 carbon atoms, inclusive; alkoxy having 1 to 4 carbon atoms, inclusive; and halogen.
 16. The process of claim 10 wherein said phosphonomethylated N-sulfonylglycine derivative is hydrolyzed in the presence of a strong acid.
 17. The process of claim 16 wherein said phosphonomethylated N-sulfonylglycine derivative is hydrolyzed by refluxing for about 1 to about 3 hours in the presence of a strong acid selected from the group consisting of hydrochloric acid, sulfuric acid and nitric acid.
 18. A process for preparing glyphosate comprising:(a) reacting sulfamic acid and chloroacetic acid in the presence of a base and at a temperature range of from about 0° C. to about 10° C. to form a N-sulfonylglycine derivative; (b) phosphonomethylating said N-sulfonylglycine derivative by reaction with formaldehyde and phosphorous acid in the presence of a solvent and with refluxing for about 1 to about 3 hours; and (c) hydrolyzing said phosphonomethylated N-sulfonylglycine derivative by refluxing in the presence of a strong acid to form glyophosate. 